Plastics such as polyesters are typically produced from petrochemical sources by well-known synthetic means. These petrochemical-based polymers take centuries to degrade after disposal. Concern over plastic waste accumulation in landfills has resulted in the recent movement toward using biodegradable polymers instead.
Synthetic biodegradable polymers, also commonly referred to as “bioplastics,” have not enjoyed great success in the marketplace due to their high production cost. However, advances in biotechnology have led to less expensive means of production. Specifically, biodegradable aliphatic copolyesters are now often produced by large-scale bacterial fermentation. Collectively termed polyhydroxyalkanoates or “PHAs”, these polymers may be synthesized in the bodies of natural or recombinant bacteria fed with glucose in a fermentation plant. Like their petrochemical precursors, the structural, and in turn mechanical, properties of PHAs may be customized to fit the specifications of the desired end product. However, unlike their petrochemical precursors, PHAs degrade both aerobically and anaerobically.
PHAs are enormously versatile, and as many as 100 different PHA structures have been identified. PHA structures may vary in two ways. First, PHAs may vary according to the structure of the R-pendant groups, which form the side chain of hydroxyalkanoic acid not contributing to the PHA carbon backbone. Second, PHAs may vary according to the number and types of units from which they are derived. For example, PHAs may be homopolymers, copolymers, and terpolymers. These variations in PHA structure are responsible for the variations in their physical characteristics. These physical characteristics allow PHAs to be used for a number of products which may be commercially valuable.
However, in order to have any type of commercially marketable PHA bioplastic product, there is a need for identifying microbial organisms that are capable of producing significant quantities of desirable PHA and to identify an efficient process for separating such PHAs from the residual biomass. Improved learnings on the biology of PHA biosynthetic pathways has allowed for the use of microbial organisms to produce significant quantities of PHA.
Numerous solvent-based and other types of extraction techniques are known in the art for extracting PHAs from bacteria and plants (biomass). Solvent-based systems (including those utilizing acetone, ketones, alone and in combination with other solvents), mechanical systems, and combinations thereof may be used for extracting PHA. However, known solvent-based systems are often inefficient and may be difficult to implement with the physical characteristics of certain PHAs (problems with gelling, degradation, etc.) More popular are two-solvent systems, but these two-solvent systems are often expensive due to the duplicated cost of solvent and may also create additional recovery steps when seeking to recover/reuse both solvents.
Therefore, there is a need for a more efficient and cost-saving process for extracting the PHA materials from biomass. Such a process would preferably involve recyclable solvents that are preferably environmentally friendly. In addition, such a process is preferably suitable to large-scale, continuous production of PHA materials.